Some low pressure fuel supply and drain rail systems for diesel engines include fuel injectors linked in series to the low pressure fuel supply and drain rail (hereinafter, the “fuel rail”). That is, fuel is delivered by the fuel rail to the first fuel injector, which passes fuel onto the next injector and so on. The fuel injectors and fuel becomes increasingly hot as the fuel passes from the first fuel injector in communication with the fuel rail to the other fuel injectors disposed downstream because heat is added to the fuel rail at each injector for a variety of reasons. For example, hot fuel spilled from a fuel injector to the surrounding injector bore in the cylinder head can generate substantial amounts of heat that is transferred back to the fuel rail. The transferred heat accumulates as the fuel moves downstream along the fuel rail. As a result, for a six cylinder engine, the fuel injectors of the fifth and sixth cylinders experience higher operating temperatures than the fuel injectors of the first and second cylinders along the fuel rail.
Various efforts to reduce emissions of diesel engines can also contribute to high operating temperatures at the fuel injectors. For example, to reduce emissions, fuel injection pressures may be increased to provide greater atomization of the fuel when it is injected into the combustion chamber. However, any leakage of high-pressure atomized fuel tends to generate heat energy at or around the fuel injector. Further, one approach used to reduce diesel emissions is to utilize multiple injections of fuel into the combustion chamber during a single combustion event. However, to accomplish multiple injections or valve movements, additional electrical energy is required. The increase in electrical energy supplied to the actuator generates some additional heat at the fuel injector but typically less heat than spilled fuel or leaked fuel.
Therefore, the combination of efforts to reduce emissions and the use of fuel rails that link fuel injectors in series can result in high operating temperatures at the fuel injectors. Excess heat can cause dimensional instability of the injectors, which, as shown in FIG. 1, are relatively complex individual devices. In general, high operating temperatures can result in unreliable performance of electrically actuated fuel injectors. Further, excess heat or high operating temperature can adversely affect the fuel by causing varnishing or lacquering of the fuel, which also adversely affects injector performance.
Some solutions to the heat problem include indirect cooling such as passing cooling water through one or more areas of the cylinder head. However, this indirect method often may not provide sufficient cooling at the fuel injectors. Other solutions include larger fuel supply pumps, larger fuel lines and fuel cooling mechanisms. However, these solutions can significantly increase the cost of an engine.